1. Field of Invention
The present invention relates to ignition circuitry for use with internal combustion engines and, more particularly, the circuits that may be used to drive a plasma-generating device.
2. Related Art
There exist several types of ignition systems for creating a spark to ignite a fuel/air mixture in combustion chamber of an internal combustion engine. A conventional ignition system typically provides a single high voltage capable of causing a discharge between the two electrodes of a conventional spark plug. Common systems for providing such a high voltage include transistorized coil ignition (TCI) and capacitive discharge ignition (CDI) systems. These systems are affective in providing the required high voltage for the initial discharge.
However, recent study has shown that spark plugs which are capable of producing a volume of plasma between the electrodes and expelling the plasma into a combustion chamber may produce better ignition efficiency as well as reducing the amount of hydrocarbon emissions of an internal combustion engine. Such spark plugs are driven by dual-stage electronics with provide an initial high voltage pulse that causes a breakdown between the electrodes to create an initial plasma kernel. A follow-on low voltage high current pulse is then provided which creates a current through the plasma. The location where the current travels through the plasma is swept outward, along with the plasma, under Lorentz and thermal expansion forces. Examples of such a spark plug as well as the associated dual stage electronics which operate in this manner are disclosed in U.S. Pat. No. 5,704,321 and U.S. patent application Ser. No. 09/204,440, both of which are hereby incorporated by reference.
In one embodiment, the present invention is directed to firing electronics which are used to provide electrical energy to a spark plug. It should be understood that while aspects of the present invention detailed below are directed to traveling spark ignitors, plasma-generating devices, and plasma-producing devices, the electronics disclosed herein may be used in conjunction with conventional spark plugs as well.
In one embodiment, an electrical circuit for providing use with a traveling spark ignitor having at least two space apart electrodes and dielectric material that fills a substantial portion of the space between the electrodes, the unfilled portion of the space between the electrodes defining a discharge gap of the ignitor is disclosed. In this embodiment, the circuit includes a conventional high-voltage ignition circuit coupled to the ignitor that provides an initial high voltage between the at least two electrodes to ionize an air/fuel mixture and form a plasma kernel in the discharge gap of the ignitor. The circuit of this embodiment also includes a secondary circuit coupled to the ignitor that a provides a follow-on current through the plasma kernel, after the initial high voltage, that expands the plasma kernel.
In some aspects, the circuit may also include a third circuit coupled to ignitor that provides an initial pulse of current to the ignitor during the follow-on current which causes the plasma kernel to begin moving away from an upper surface of the dielectric material.
In another embodiment, a circuit for providing a follow-on current between the electrodes of a traveling spark ignitor after an initial break down between the electrodes has occurred is disclosed. In this embodiment, the circuit may include a first capacitor coupled in parallel to a secondary side of an ignition coil and the ignitor and a blocking element serially coupled between the first capacitor and the ignitor. The circuit of this embodiment may also include a second capacitor coupled in parallel with the ignitor and an inductive element serially coupled between the second capacitor and the ignitor.
In another embodiment a method of operating a traveling spark ignitor is is disclosed. The method of this embodiment includes steps of: (a) providing a first high voltage between electrodes of the ignitor to form a plasma kernel, (b) providing a follow-on current between the electrodes and through the plasma kernel causing the plasma kernel to expand and be swept out of the ignitor due to a Lorentz force and (c) during step (b) providing a first high current during a first time period of the follow-on current at causes the plasma kernel to begin moving outwardly.